Group Leader

The project aims at: a) the better understanding of the paleoenvironmental –geoarchaeological conditions predominated in the “Hellenic Lands” (Greek Mainland and the surrounding islands) that influenced the diachronically evolving landscape of the areas under investigation, since the Paleolithic till the recent years, b) the investigation of the energy states and the chronometry of ancient natural and artificial materials by employing the currently developing dating techniques of luminescence, c) increasing our knowledge on the technologies and practices once followed by the ancients for the mining, extraction, production, transformation, alloying and trading of ancient metals and associated objects, since the early times onwards, d) research and application for the restoration of ancient and historic metallic implements by physicochemical reduction and dechlorination, achieved by exploitation of modern plasma techniques.

Luminescence dating

Luminescence dating either as Optically Stimulated Luminescence, OSL, or as Thermo-Luminescence, TL, is widely applied and appropriate when other chronometric techniques are not possible. The technique exploits the emission of light released from some minerals such as quartz or feldspars, which are rather common components of most rocks in the earth’s surface. In the case of OSL sediment dating, suitable material (sand or silt-sized grains of quartz and feldspar) is usually available ubiquitously throughout the site. The OSL clock, like in TL dating, is reset by exposure to sediment to sunlight prior to deposition. An advantage of OSL dating is that the luminescence of quartz and feldspar grains is reduced to a low definable level after a few minutes of sunlight exposures versus hours for the corresponding TL response.

Two major parameters are required and measured for the calculation of an age by the luminescence techniques; a) the total energy accumulated due to the constant action of the environmental radioactivity over the years during which an object is buried (or a layer of sediment is deposited) and b) the radioactivity that affects and absorbed by the ‘datable’ material during one year. What is estimated by employing the optically stimulated techniques is the time elapsed since the last sunlight exposure (deposition) and the measurement in the laboratory. OSL dating uses light of a particular wavelength or range of wavelengths, usually blue, green or infrared light, releasing rapidly the most light sensitive trapped electrons from the crystal lattice. The age range for pottery and other ceramics covers the entire period in which these materials have been produced (up to 8,000 years). The typical range for burnt stone or sediment is from about 100 to 300,000 years. The error limits on the dates obtained are typically in the range of 8 to 12%.

Recent advances of the LUM dating techniques, now applied in the laboratory, such as thermally transferred OSL, TTOSL, isothermal thermoluminescence from quartz, ITL, and post-infrared/infrared stimulated luminescence from feldspars (p-IR-IRSL) allow increased dating reliability, total error elimination and age determinations of sediments as old as 1,000,000 years or even older.

The implementation of the ongoing sub-projects falling in the fields of paleoenvironment and geoarchaeology very often employs the techniques of luminescence chronometry. This happens for two reasons a) carbonized remains (that might be dated by radiocarbon) are rather uncommon in the earthen formations that are geoarchaeologically studied and b) the ages required to be determined in the paleoenvironmental studies are usually very big, far beyond the lower limit of radiocarbon (~50,000a), with the natural phenomena (e.g. past volcanic eruptions) sought to be dated usually happened half million of years ago or even earlier. Similar applications are routinely required in speleothems luminescence dating from subsurface karst formations or in archaeo-seismic studies; in the latter cases if cross-checking of obtained ages is essential, the application of the ESR (electron spin resonance) dating technique might be, additionally applied in the laboratory.

Restoration & conservation of metallic artifacts by Plasma techniques

In addition to studies dealing with ancient mining and metallurgy (ore digging out, archaeomining technology assessment, beneficiation, ancient extractive metallurgy/pyrometallurgy, studies of ancient slags, alloying, archaeometallurgical experiments/simulations of smelting practices, metals provenancing etc), a considerable part of the laboratory activities is driven to research and applications for metals restoration, surface cleaning and dechlorination by employing plasma physicochemical techniques. The stabilisation treatment via hydrogen glow discharge plasma (HGDP) at low temperature and pressure on different metallic substrates is one of the main activities of plasma laboratory at the INN. In addition to iron-based pieces of Art that were treated on the past, the research and applications was expanded by the study of the corrosion layers of copper alloys and their reduction using HGDP during the last years.

Copper alloys, depending on the corrosive environment, may exhibit a variety of corrosion products. The most aggressive environments are those rich in chlorine species due to the instability that their presence imparts to the metallic surface. Thus, the removal of these species from the surface of bronze artefacts is very important in order to inhibit a self-accelerated corrosion process known as “bronze disease”. Representative ancient-like bronzes were employed for the chemical synthesis of Cu2(OH)3Cl rich patinas in order to study the influence of the alloying elements in the evolution of the chloride attack and to further conduct reduction of the different corrosion oxides using plasma chemistry methods. It is not only the chemical composition of an alloy that affects both the corrosion profile and the cleaning treatment efficiency; different metallurgical characteristics such as the composition and size of dendritic formations can create microgalvanic phenomena during the corrosion process. Thus surfaces of extensive heterogeneity are produced, which greatly complicate every effort to understand how these “subsystems” contribute to the overall corrosion mechanism and to apply a suitable stabilization treatment. Although there is a considerable number of chemical treatments for the conservation of copper, bronze, and brass, most are not satisfactory for cupreous metals recovered from marine sites. Taking into account effectiveness and what patination changes are acceptable, traditional methods exhibit many disadvantages as conservation techniques are frequently very laborious, and if chemical treatments are used to replace intricate manual work, it is difficult to ensure sufficient control and selectivity.

The reduction of corrosion layers employing the HGDP techniques is considered as a novel technique compared to the traditional cleaning treatments applied on copper alloys, although its initial application to metals conservation dates back to 1979. The method is based on the reduction of the corrosion products, at low pressure and temperature, by chemically reactive species such as ions and radicals, which are produced in electrical discharges with the use of a gas or a mixture of gases.

Three representative ancient like cast bronzes (one rich in Sn, one rich in Zn, and one rich in Pb) were employed as substrates in order to study the influence of the alloying elements in the evolution of corrosion. The corrosion behavior of specimens having Sn and Pb as main alloying elements is governed by a decuprification mechanism and by the formation of Sn–Pb–O enriched barrier layers. In the case of the Zn containing alloy, dezincification is more pronounced at the corrosion initial stages, and copper species predominate the corrosion products evolution. A three-hour HGDP treatment leads to Cu+ production and metallic Cu, Sn, Zn, and Pb redeposition, as a result of metal cation reduction. This process is accompanied by partial removal of Cl species, O diminution, and change in coloration. The further increase of the Cl/O atomic ratio measured on the post-treated surfaces leads to the formation of nantokite and thus to the conclusion that the stabilization of objects with extensive Cl attack is not feasible by HGDP without preliminary chemical treatment. Marine objects with cultural importance were for the first time restored at the Plasma Physics Laboratory/INN, in the frame of a collaboration with the Chemical Engineering School of the National Technical University of Athens. Other ongoing collaborations have been undertaken with the Technological & Educational Institute of Athens/Dept of Antiquities and Works of Art Conservation, the Byzantine-Christian Museum and other known Greek or foreign Institutions.

Infrastructure

One RISØ-DA-15, TL/OSL luminescence reader for absolute dating purposes, two dark rooms for sample preparation and released luminescence measuring.

Two devices-‘reactors’ for glow radiofrequency plasma creation with low pressure and temperature, designated for smaller and for bigger metallic objects.

Optical polarizing microscopes working with both incident and transmitting light, as well as stereo-microscopes with photo-documentation devices, for microphsaes characterization, metallographic analysis, tissue and intergrowth studying of metallic objects, archeaometallurgical residues and other archaeomaterials.

New software (DRc) for data manipulation and appropriate for dating studies employing luminescence techniques or for ESR-dating. Also software for satellite images interpretation and for GIS applications.

Complete equipment for laboratory and field metallurgical experiments for metal production, based on prehistoric and ancient practices of the Aegean and the wider Mediterranean region.

Application of plasma techniques for conservation, reducing restoration, dechlorination and surface cleaning of metallic objects (iron, copper and relevant alloys, lead and silver).

Studies and expert’s advices on authenticity of archaeological objects and of artefacts with questionable historical/archaeological/financial value.

Training of conservators for the applications of the plasma-chemistry restoration techniques, organization of archaeometric training courses and offering of laboratory instruction to personnel of foreign Schools, groups of postgraduate students etc.